If you order straight run it really is a gamble. I've heard the occasional story of someone getting ALL cockerels. While I think that's possible, I think it's probably unusual. Usually you get some mix of males and females. If you aren't allowed roosters where you live, don't have room to house extra roosters, don't have the ability to keep them separate should they not get along with each other, don't care about having fertilized eggs, can't bear the thought of selling or giving your extra cockerels away to someone who might eat them, or don't want to process and eat them yourself, then I would pay the extra to get sexed chicks. You still might get a surprise rooster that "slipped by" the inspectors, but it is not likely. Watch out though, some hatcheries will add "packing peanut" chicks into your order. This happens more often if you order a small number of chicks or you order them early when the weather is cold. The hatchery adds these extra chicks in to keep the others warm to decrease the chance that some die during shipment. These extra chicks are almost always males that the hatchery would have disposed of anyways. Some hatcheries have policies against sending extra chicks, and some will only send them if the orders are small. You can call the hatchery directly to find out before ordering so you don't end up with any surprises.
If you are planning on free ranging, you may want to have at least one rooster. (Most) Roosters keep a very watchful eye out for anything that will harm their ladies. They can make excellent "early warning systems" against predators, buying your hens valuable seconds to take cover if something attacks. While they are no match for large predators like foxes, coons, coyotes, etc., they have been known to take on a hawk successfully, even coming to the aid of their hens. If I weren't keeping contraband chickens in the first place, I would have kept the roo that was gifted to me. He did a good job of sounding the alarm when hawks and crows circled overhead. Roos are different than hens, they are usually more standoffish and some can be downright mean, so keep that in mind when you are selecting a breed. Preferably, get a roo from a line of birds that is known for good temperament and the odds of getting a friendly (or at least not nasty) rooster will be higher.